It has long been known that peroxygen bleaches are effective for stain and/or soil removal from fabrics, but that such bleaches are temperature dependent. At a laundry liquor temperature of 60.degree. C., peroxygen bleaches are only partially effective. As the laundry liquor temperature is lowered below 60.degree. C., peroxygen bleaches become relatively ineffective. As a consequence, there has been a substantial amount of industrial research to develop bleaching systems which contain an activator that renders peroxygen bleaches effective at laundry liquor temperatures below 60.degree. C.
Numerous substances have been disclosed in the art as effective bleach activators. One widely-used bleach activator is tetraacetyl ethylene diamine (TAED). TAED provides effective hydrophilic cleaning especially on beverage stains, but has limited performance on dingy stains and body soils. Another type of activator, such as nonanoyloxybenzenesulfonate (NOBS) and other activators which generally comprise long chain alkyl moieties, is hydrophobic in nature and provides excellent performance on dingy stains. However, many of the hydrophobic activators developed thus far can promote damage to natural rubber parts used in certain washing machines and to natural rubber articles exposed to the activators. Because of these negative effects on natural rubber machine parts and articles, the selection of such detergent-added bleaching systems has been limited.
It has now been determined that in conventional bleaching systems, particularly those comprising a hydrophobic bleach activator and a source of hydrogen peroxide, the bleach activator undergoes perhydrolysis to form a peroxyacid bleaching agent. A by-product of the perhydrolysis reaction between such bleach activators and hydrogen peroxide is a diacylperoxide (DAP) species. It has now further been discovered that the DAP's derived from hydrophobic activators tend to be insoluble, poorly dispersible, oily materials which form a residue which can deposit on the natural rubber machine parts that are exposed to the laundry liquor. The oily DAP residue can form a film on the natural rubber parts and promote free radical and peroxide damage to the rubber, which eventually leads to failure of the part. This is particularly true of rubber parts which have prolonged exposure to the laundry liquor, such as sump hoses.
By the present invention, is has now been discovered that the class of bleach activators derived from acyl valerolactams forms peroxyacids upon perhydrolysis without the production of oily, harmful DAP's. Without intending to be limited by theory, it is believed that the bleach activators employed herein provide good cleaning performance with safety to natural rubber, since they do not expose the natural rubber machine parts or articles to DAP oxidation. Whatever the reason, natural rubber parts and articles remain substantially undamaged by the bleaching systems of the present invention.
By the present invention, it has also now been discovered the bleach activators of this invention provide dingy soil clean-up and enhanced nucleophilic and body soil removal. Furthermore, the bleaching systems and activators herein are effective at low concentration levels and at temperatures below 60.degree. C. when used in the manner provided by this invention. In addition, the activators herein have better perhydrolysis speed and yield when compared to other lactam bleach activators, such as acyl caprolactam activators.
Accordingly, the present invention presents an effective, color-safe bleaching system which does not promote damage to natural rubber parts in washing machines or damage to natural rubber articles.